Myositis is an inflammatory autoimmune condition that can cause muscles to become weak and painful. Idiopathic inflammatory myopathies are an umbrella term for the different types of myositis. These autoimmune conditions mean the body attacks its own muscles, connective tissue, blood vessels, skin, lungs, and other organs. This often occurs together with other symptoms, such as muscle swelling, pain, fatigue, difficulty moving limbs or lifting arms, increased falls, trouble swallowing, and others.